This proposal examines 2 questions. (1) What are the molecular features of gastric epithelial lineage progenitors and how are they affected by parietal cell loss? (2) What role does attachment of Helicobacter pylori to these progenitors play in defining the outcome of H. pylori infection? These investigators have developed a transgenic mouse (toxl 76) where ablation of parietal cells leads to progressive amplification of these progenitors. The progenitors produce NeuAcalpha2,3Galbeta 1,4-glycans that serve as receptors for H. pylori adhesins in vivo. These glycans are also found in human gastric Ca and its precursors. The results suggest that when the relationship between host and H. pylori results in loss of parietal cells, as in chronic atrophic gastritis (CAG), H. pylori tropism to lineage progenitors may occur if there is a matching of H. pylori adhesin and host receptor production. Binding to amplified progenitor cells may then help facilitate initiation and/or progression of tumorigenesis. The investigators will explore this hypothesis using gnotobiotic toxl 76 mice and test its clinical relevance using materials from a completed Swedish case control study of H. pylori-infected patients with Ca + CAG. There are 3 related aims: 1). Obtain a molecular signature of lineage progenitors and of parietal cells. Identify parietal cell factors that affect the progenitors. Lectin panning will be used to recover these cells. Cellular RNA will be probed with Affymetrix GeneChips to identify (i) a panel of molecular markers of these cell types; and (ii) genes expressed in parietal cells that may affect the proliferative status/census of progenitors. The effects of candidates selected from (ii) will be tested directly by gene knockout. 2). Determine the molecular responses of the host when H. pylori interacts with NeuAc-alpha2,3Gal-beta1,4+ progenitors. Germ-free normal and toxl76 mice will be colonized with an H. pylori isolate that produces adhesins that bind to NeuAc-alpha2,3Gal-beta1,4+ progenitors. GeneChips will be used to profile host gene expression before and after colonization. The role of mucosal immune cells in the host response will be examined by gene expression profiling of gnotobiotic Ragl-/normal + toxl76 mice. The impact of manipulating expression of the adhesin responsible for progenitor cell attachment will be tested. 3). H. pylori isolates from the case control study will be used to characterize H. pylori genes that affect host responses. Isolates will be tested for their binding to NeuAc-alpha2,3Gal-beta 1,4 glycans. Whole genome genotyping of binding isolates from cases with Ca + CAG, and from controls + CAG will be performed using DNA arrays containing 1661 amplified OREs from the sequenced H. pylori 26695 and J99 strains. Isolates with representative genotypes associated with CAG and Ca will be selected from the panel (or genetically engineered), introduced into toxl76 mice, and host responses defined. These studies should yield new insights about H. pylori pathogenesis plus markers for identifying patients at risk for severe pathology.